The present invention generally relates to photochromic materials, and more particularly relates to photochromic materials comprising an indeno-fused naphthopyran and a metallocenyl group bonded to the indeno-fused naphthopyran. The present invention further relates to photochromic compositions and articles that comprise such photochromic materials.
Photochromic materials undergo a transformation from one form (or state) to another in response to certain wavelengths of electromagnetic radiation, with each form having a characteristic absorption spectrum for visible radiation. For example, thermally reversible photochromic materials are capable of transforming from a ground-state form to an activated-state form in response to actinic radiation, and reverting back to the ground-state form in response to thermal energy and in the absence of the actinic radiation. As used herein, the term “actinic radiation” refers to electromagnetic radiation that is capable of causing a photochromic material to transform from one form or state to another.
Photochromic materials adapted for use in ophthalmic applications appear to be essentially colorless or “optically clear” when not exposed to actinic radiation (i.e., in the ground-state form) and exhibit a visible color that is characteristic of the absorption spectrum of the activated-state form of the photochromic material upon exposure to actinic radiation. Photochromic compositions and articles that contain one or more photochromic materials, for example photochromic lenses for eyewear applications, may display clear and colored states that generally correspond to the optically clear and colored states of the photochromic material(s) that they contain.
More particularly, for single band absorbing photochromic materials, as specific wavelengths within the visible region of electromagnetic radiation are absorbed by a photochromic material in the activated-state form, the wavelengths within the visible region that are transmitted (i.e., not absorbed) correspond to the color of the photochromic material in the activated-state form. Absorption of light having wavelengths above 500 nm to around 520 nm in the visible region of the electromagnetic spectrum results in a photochromic material that exhibits a “red” or “reddish” color, i.e., it absorbs visible radiation from the short wavelength or “blue end” of the visible spectrum and transmits radiation from the longer wavelength or red end of the visible spectrum. Conversely, absorption of light having wavelengths around 580 nm to around 610 nm in the visible region of the electromagnetic spectrum results in a photochromic material that exhibits a “blue” or “bluish” color, i.e., it absorbs visible radiation from the longer wavelength or “red end” of the visible spectrum and transmits radiation from the shorter wavelength or blue end of the visible spectrum. Photochromics having broad-band absorption, that is displaying more than one absorption maximum in the visible region, will tend to exhibit a blended color.
Many current photochromic compounds exhibit red (or reddish) or blue (or bluish) colors. However, for certain applications it may be desirable to have a photochromic material that has a characteristic color other than red or blue. For example, for some ophthalmic applications, it may be desirable to have a photochromic material that has a characteristic green color.
Further, for many applications, it may be desirable that the photochromic material be able to make the transition from the colored activated-state form to the optically clear ground-state form as quickly as possible. For example, in photochromic eyewear applications, ophthalmic lenses comprising photochromic materials may transform from an optically clear state to a colored state as the wearer moves from a region of low actinic radiation, such as indoors, to a region of high actinic radiation, such as into direct sunlight. As the lenses become colored, less electromagnetic radiation having wavelengths within the visible and/or ultraviolet regions of the electromagnetic spectrum is transmitted through the lens to the wearer's eyes. In other words, more electromagnetic radiation is absorbed by the lenses in the colored state than in the optically clear state. When the wearer subsequently moves from the region of high actinic radiation back to a region of low actinic radiation, the photochromic material in the eyewear reverts from the colored, activated-state form to the optically clear, ground-state form in response to thermal energy and the absence of actinic radiation. If, once removed from actinic radiation, the transition from the colored state to the clear state takes several minutes or more, the wearer's vision may be less than optimal during this time due to the combined effects of the lower ambient light and the reduced transmission of visible light through the colored lenses. Accordingly, for certain application, it may be advantageous to develop photochromic materials that may more quickly transition from the optically clear ground state-form to the colored activated-state form and/or transition from the colored activated-state form to the optically clear ground state-form as compared to conventional photochromic materials.